Hemagglutinin (HA) is an envelope protein of the influenza virus (an orthomyxovirus), and is the prototypic RNA virus Class I fusion protein. HA is produced in infected cells as a precursor protein HA0 which is proteolytically cleaved into 2 proteins referred to as HA1 and HA2. HA2 contains an amino terminal hydrophobic domain, referred to as the fusion peptide, which is exposed during cleavage of the hemagglutinin precursor protein. Retroviral transmembrane proteins contain several structural features in common with the known structure of HA2 in addition to the fusion peptide, including an extended amino-terminal helix (N-helix, usually a “heptad repeat” or “leucine zipper”), a carboxy-terminal helix (C-helix), and an aromatic motif proximal to the transmembrane domain. The presence of at least four out of these five domains defines a viral envelope protein as a Class I fusion protein.
FIG. 1 shows six identified domains of the fusion proteins of the six families of Class I viruses. The fusion proteins originate in a hydrophobic fusion peptide, terminate in an anchor peptide, and incorporate an extended amino terminal alpha-helix (N-helix, usually a “heptad repeat” or “leucine zipper”), a carboxy-terminal alpha-helix (C-helix), and sometimes an aromatic motif proximal to the virion envelope. The sixth domain, referred to herein as the fusion initiation region (FIR), which is disclosed in U.S. Pat. Nos. 7,491,793 and 8,222,204 (to Garry and Wilson), each of which is incorporated herein by reference in its entirety.
There are multiple subtypes of the influenza A virus. Each viral subtype comprises one specific combination of versions of two glycoproteins that are embedded in the lipid membrane envelopes of the viruses. The two subtype-defining glycoproteins are hemagglutinin HA and neuraminidase (NA). There are seventeen known variants of HA, which are referred to as H1 through H17, respectively, and nine known variants of neuraminidase, which are referred to as N1 through N9, respectively. Each viral subtype is specified characterized by its hemagglutinin and neuraminidase variant numbers, respectively. For example, influenza A subtype H3N2 is a swine flu, and subtype H5N1 is an avian flu.
About 10 to 20 percent of the population of the United States suffers from seasonal influenza each year. While most individuals recover from influenza in one to two weeks, the very young, the elderly, and persons with chronic medical conditions can develop post-flu pneumonia and other lethal complications. The causative agent of influenza is the influenza virus, an orthomyxovirus that readily develops new strains through a process of reassortment and mutation of the segmented viral genome.
The FIR of Class I viruses is the region of the viral fusion envelope proteins involved in virus envelope-to-host cell membrane fusion, which is the process by which a host cell membrane-bound virus interrupts the integrity of the host cell membrane to inject the genetic material of the virus into the host cell. This process involves a merger of the viral envelope and a host cell membrane, which is mediated by the viral fusion protein (e.g., hemagglutinin in the case of influenza viruses), thus exposing the interior of the host cell to the interior of the virus. As disclosed in U.S. Pat. Nos. 7,491,793 and 8,222,204 (to Garry and Wilson) mentioned above, relatively short peptides comprising or consisting of a segment of the FIR can bind to a virus fusion protein and interfere with conformational changes required for fusion to occur. Such peptides thus prevent infection of the host cells by the viruses, despite the fact that the viruses can still bind to the surface of the host cell membrane. Thus, the FIR peptides inhibit viral infectivity by an entirely different mechanism than traditional vaccine treatments, which generally involve production of antibodies that prevent binding of the virus with the host cell, rather than interfering with the biochemical events that comprise the vial fusion mechanism, per se.
Highly virulent strains of type A influenza virus can produce epidemics and pandemics. In recent years, there has been an emergence of a highly pathogenic strain of avian influenza A virus subtype H5N1 capable of inflicting a high mortality rate. Dealing with the threats posed by the influenza virus both to public health and as a potential agent of bioterrorism are high priorities. Consequently, there is an ongoing need to develop treatment compositions and methods to control seasonal influenza and the increasing threat of pandemic influenza and weaponized influenza. The peptide conjugates, antibodies, and described herein address these needs.